diff --git a/app/Ai/Agents/SocialMediaAssistant.php b/app/Ai/Agents/SocialMediaAssistant.php
index 0c1861e1..ba55e4fb 100644
--- a/app/Ai/Agents/SocialMediaAssistant.php
+++ b/app/Ai/Agents/SocialMediaAssistant.php
@@ -4,9 +4,12 @@
 
 namespace App\Ai\Agents;
 
+use App\Ai\PlatformRules\Contract;
+use App\Ai\PlatformRules\Registry as PlatformRulesRegistry;
 use App\Ai\Tools\GenerateAudio;
 use App\Ai\Tools\GenerateImage;
 use App\Ai\Tools\GenerateVideo;
+use App\Enums\SocialAccount\Platform;
 use App\Models\AiMessage;
 use App\Models\Post;
 use App\Models\Workspace;
@@ -37,9 +40,31 @@ public function instructions(): string
             'tone' => $this->workspace->brand_tone ?? 'professional',
             'voice_notes' => $this->workspace->brand_voice_notes ?? '',
             'locale' => app()->getLocale(),
+            'platform_rules' => $this->activePlatformRules(),
         ])->render();
     }
 
+    /**
+     * @return array<int, Contract>
+     */
+    private function activePlatformRules(): array
+    {
+        if (! $this->post) {
+            return [];
+        }
+
+        $platforms = $this->post->postPlatforms
+            ->pluck('platform')
+            ->filter()
+            ->map(fn ($p) => $p instanceof Platform ? $p : Platform::tryFrom((string) $p))
+            ->filter()
+            ->unique(fn (Platform $p) => $p->value)
+            ->values()
+            ->all();
+
+        return PlatformRulesRegistry::forMany($platforms);
+    }
+
     /**
      * @return iterable<Message>
      */
diff --git a/resources/views/prompts/assistant/platforms.blade.php b/resources/views/prompts/assistant/platforms.blade.php
new file mode 100644
index 00000000..7e7fd977
--- /dev/null
+++ b/resources/views/prompts/assistant/platforms.blade.php
@@ -0,0 +1,9 @@
+@if(count($platform_rules) > 0)
+ACTIVE PLATFORMS FOR THIS POST:
+The user is creating a post targeting the following platform(s). Tailor content length, format, and tone to these constraints.
+
+@foreach($platform_rules as $rule)
+{{ $rule->summary() }}
+
+@endforeach
+@endif
diff --git a/resources/views/prompts/assistant/system.blade.php b/resources/views/prompts/assistant/system.blade.php
index fcd8ed40..6d234d85 100644
--- a/resources/views/prompts/assistant/system.blade.php
+++ b/resources/views/prompts/assistant/system.blade.php
@@ -29,46 +29,7 @@
 - You ONLY help with social media content creation.
 - If the user asks about anything unrelated, politely decline and redirect to content creation.
 
-PLATFORM KNOWLEDGE:
-You must understand each platform's formats, constraints, and best practices to create optimal content.
-
-Instagram:
-- Feed Post: square (1:1) or portrait (4:5). Up to 10 images/videos. Caption max 2200 chars. 30 hashtags max (3-5 recommended).
-- Carousel: same as Feed Post with 2-10 slides. All slides share the same aspect ratio. First slide is the hook. Great for educational/step-by-step content.
-- Reel: vertical 9:16 only. Video only. Up to 90 seconds (30-60s performs best). Hook in first 1-3 seconds.
-- Story: vertical 9:16. Single image or video. Disappears after 24h. Use CTAs and interactive elements.
-
-Facebook:
-- Post: flexible aspect ratio. Up to 10 images. Caption up to 63,206 chars (but short posts perform better). Text-only allowed.
-- Reel: vertical 9:16. Video only. Up to 90 seconds. Similar to Instagram Reels.
-- Story: vertical 9:16. Single image or video. Disappears after 24h.
-
-X (Twitter):
-- Post: max 280 characters. Up to 4 images or 1 video. Landscape 16:9 or square 1:1 for images. Concise, punchy copy.
-
-TikTok:
-- Video: vertical 9:16 only. Video only. 15-60 seconds performs best. Hook in first 1-2 seconds. Trendy, authentic style.
-
-YouTube:
-- Short: vertical 9:16. Video only. Up to 60 seconds. Loop-friendly content. Hook immediately.
-
-LinkedIn:
-- Post: max 3000 chars. 1 image/video. First 2-3 lines visible before "see more" — make them compelling. Professional tone.
-- Carousel: PDF-based document with swipeable slides. Up to 20 slides (8-12 optimal). Images only. Educational content performs extremely well.
-
-Threads:
-- Post: max 500 chars. Up to 10 images/videos. Conversational tone. Ask questions to drive replies.
-
-Pinterest:
-- Pin: portrait 2:3 (1000x1500px). Single image. Title max 100 chars, description max 500 chars. Use text overlay on images.
-- Video Pin: vertical 9:16 or portrait 2:3. 4 seconds to 15 minutes.
-- Carousel: portrait 2:3. Up to 5 images. Images only.
-
-Bluesky:
-- Post: max 300 chars. Up to 4 images or 1 video. Similar to X but shorter.
-
-Mastodon:
-- Post: max 500 chars. Up to 4 images or 1 video.
+@include('prompts.assistant.platforms')
 
 CONTENT CREATION RULES:
 - When the user mentions a specific platform, tailor the content to that platform's constraints and best practices.
diff --git a/tests/Feature/Ai/SocialMediaAssistantTest.php b/tests/Feature/Ai/SocialMediaAssistantTest.php
index fd906dde..1f132bdc 100644
--- a/tests/Feature/Ai/SocialMediaAssistantTest.php
+++ b/tests/Feature/Ai/SocialMediaAssistantTest.php
@@ -3,10 +3,13 @@
 declare(strict_types=1);
 
 use App\Ai\Agents\SocialMediaAssistant;
+use App\Enums\SocialAccount\Platform;
 use App\Enums\User\Setup;
 use App\Enums\UserWorkspace\Role;
 use App\Models\AiMessage;
 use App\Models\Post;
+use App\Models\PostPlatform;
+use App\Models\SocialAccount;
 use App\Models\User;
 use App\Models\Workspace;
 use Laravel\Ai\Enums\Lab;
@@ -97,6 +100,34 @@
     expect($messages[0]->content)->toContain('[This assistant message attached: 2 image]');
 });
 
+test('instructions include rules only for active post platforms', function () {
+    $socialAccount = SocialAccount::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'platform' => Platform::X,
+    ]);
+
+    PostPlatform::factory()->create([
+        'post_id' => $this->post->id,
+        'social_account_id' => $socialAccount->id,
+        'platform' => Platform::X,
+    ]);
+
+    $agent = new SocialMediaAssistant($this->workspace, $this->post->fresh('postPlatforms'));
+
+    $instructions = $agent->instructions();
+
+    expect($instructions)->toContain('X (Twitter): 280 chars');
+    expect($instructions)->not->toContain('Instagram: caption max 2200');
+});
+
+test('instructions include no platform rules section when post has no platforms', function () {
+    $agent = new SocialMediaAssistant($this->workspace, $this->post);
+
+    $instructions = $agent->instructions();
+
+    expect($instructions)->not->toContain('ACTIVE PLATFORMS FOR THIS POST');
+});
+
 test('provider honors trypost.ai.text_provider config', function () {
     config()->set('trypost.ai.text_provider', 'openai');